A wide variety of mesogenic or rigid rodlike containing monomers and the various polymerization products thereof are well known. Representative of these monomers re those taught by Conciatori, et. al. in U.S. Pat. No. 4,514,553 where hydroxyaromatic carboxylic acids are first esterified with an acrylic acid chloride, the resulting acrylic terminated aromatic carboxylic acid is converted to the corresponding carboxylic acid chloride, then coupling with a diphenol provides an acrylate terminated monomer. Although the monomers resulting from this process are reported to be anisotropic, all are solids, with melting points ranging from 60.degree. C. to 154.degree. C., and are therefore not readily processable as curable liquids.
Vinyl esters are the reaction product of about equivalent amounts of a monounsaturated monocarboxylic acid and a polyepoxide. One class of vinyl esters is described by Bearden in U.S. Pat. No. 3,367,992 where dicarboxylic acid half esters of hydroxyalkyl acrylates or methacrylates are reacted with polyepoxide resins. Bowen in U.S. Pat. Nos. 3,066,112 and 3,179,623 describes the preparation of vinyl esters from monocarboxylic acids such as acrylic or methacrylic acid. Bowen also describes alternate methods of preparation wherein a glycidyl methacrylate or acrylate is reacted with the sodium salt of a dihydric phenol such as bisphenol A. Vinyl ester resins based on epoxy novolac resins are described in U.S. Pat. No. 3,301,743 to Fekete, et. al. Fekete, et. al. describe vinyl esters where the molecular weight of the polyepoxide is increased by reacting a dicarboxylic acid with the polyepoxide resin as well as acrylic acid, etc. in U.S. Pat. No. 3,256,226. Polymer modified vinyl esters are described by Najvar in U.S. Pat. No. 3,892,819 where carboxylic acid terminated rubber replaces part of the methacrylic acid reacted with polyepoxide resins. Other functional compounds containing a group reactive with an epoxide group, such as an amine, mercaptan and the like, may be utilized in place of the dicarboxylic acid. All of the above described compositions, which contain the characteristic linkage. ##STR1## and terminal vinyl or vinylidene groups are classified as vinyl esters. The vinyl esters thus prepared are typically combined with a reactive diluent, a copolymerizable vinyl monomer, to alter the viscosity of the mixture, to vary properties of the cured resin, or for other known reasons. Both the vinyl ester and the vinyl ester resin, i.e. the blend with a copolymerizable vinyl monomer, are curable (thermosettable), typically, by mixing in a free radical forming catalyst and applying heat and/or adding an accelerator.
The vinyl ester resins of the present invention contain one or more mesogenic or rigid rodlike side chain moieties which impart substantial mechanical property enhancement to the cured compositions thereof. Additional compositions of the present invention simultaneously contain both side chain and main chain mesogenic or rigid rodlike moieties. Further compositions of the present invention contain only a main chain mesogenic or rigid rodlike moiety. The presence of the mesogenic or rigid rodlike moiety manifests itself through enhanced mechanical strength, notably tensile and flexural strength/modulus, in the cured products. The invention consists of the vinyl esters and the vinyl ester and polymerizable ethylenically unsaturated monomer formulations, whether or not cured.